Deregulation of the airline industry has resulted in reduced airfares, which when combined with stable fuel prices that has produced a volume of air travel that has been strongly and steadily increasing in the past decade, and this trend is expected to continue unabated over the next two decades. Airport support infrastructure, however, has not kept pace with increasing traffic volume, and is expected to lag further in the coming decades. With limited numbers of airport gates, there is a strong motivation for airlines to move to larger aircraft to accommodate increased passenger volume through a limited number of gates. The need for larger aircraft is particularly critical at major “hub” airports in the “hub and spoke” systems operated by most large airlines in order to maximize passenger flow through their limited airport facilities.
A significant problem with larger aircraft is that it may be difficult to physically accommodate the increased wingspan in airport gates and taxiways designed for smaller aircraft. Increased wingspan for the larger aircraft is also highly desirable in view of the substantially improved aerodynamic efficiency and payload-range characteristics that are associated with increased wingspan. The increased wingspan and/or length of larger aircraft will make parking such aircraft next to each other at gates more risky in terms of probability of collision, and will also increase problems related to ground service vehicle, arrangements, flows, and congestion. Similarly, the increased wingspan increases the probability of collisions between aircraft taxiing on taxiways/taxilanes or other fixed objects,
Several prior art approaches exist, which address the problems associated with fitting larger aircraft into airport facilities originally designed for smaller aircraft. One obvious approach to maximizing passenger volume capability at a limited number of airport gates has been to park the largest possible aircraft type that will “fit” at each gate, given the constraining requirements of minimum clearances between the parked aircraft's wingtips and the wingtips of adjacent parked or parking aircraft and between the parked aircraft's aftmost extremity (e.g., tip of tail) and the “parking limit line” which separates the parking area from an adjacent active taxilane. This is a reasonable approach, but is inherently limited in the amount of additional passenger volume it can develop. Airline fleet mix, and more particularly the fleet mix present at each hub complex (i.e., the mix of aircraft actually present simultaneously at a gate constrained hub airport), can reduce the effectiveness of this strategy in increasing passenger volume. Airport terminals with movable (i.e., apron-drive type) passenger boarding bridges can take advantage of this method to a considerably greater extent than can airport terminals with fixed boarding bridges, because movable bridges can be moved to effectively change the maximum aircraft size accommodatable at each gate.
A second prior art approach has been to reduce the allowable operational clearances between parked aircraft and between a given aircraft and other fixed or moving objects (including other aircraft). An FAA Advisory Circular 150/5300-13 CHG 6, Sep. 30, 2000 specifies minimum clearances to be assumed for airport facilities design and expansion purposes. The specified clearance between a taxiing aircraft's wingtip and a nearest fixed-or-movable object is 44 ft. for Group IV airplanes (e.g., 767 or DC-10 class). Current airline practice includes examples of wingtip-to-wingtip clearances of as low as 17 ft. between adjacent parked aircraft or between two aircraft on parallel taxiways. An obvious disadvantage of this second approach is that it increases the probability of collisions, and requires increased pilot attention and precision for the taxiing and parking tasks.
A third prior art approach is to alternate large and small aircraft (747's and 737's) at gates nominally designed for 767/DC-10 size aircraft. While this approach increases the size of the largest accommodatable aircraft, it has the disadvantage that it may not significantly increase total passenger volume accommodatable, for example total passengers for 5 747's and 5 737's may not be significantly greater than for 10 DC-10's.
A fourth prior art approach goes beyond reducing allowable clearances between aircraft or alternating large and small aircraft. By taking into account the vertical separation between wingtips. For example, a DC-10 could be parked adjacent to a 727 with zero or even negative wingtip separation in a plan view, but with no real wing interference if the 727 wingtip passes under the DC-10 outer wing. Adequate vertical clearances have to be established accounting for the lowest possible ground clearance for the DC-10 wing and the highest possible wingtip location for the 727 (e.g., due to weight, gusts, etc.). The disadvantages of this approach are that it requires that airplanes with adequate vertical clearances be alternately parked, it limits gate assignment flexibility, and (ii) it aggravates problems of ground service vehicle access and parking.
A fifth prior art approach has been to use angled parking of aircraft at the gate combined with carefully designed nonlinear (e.g., curved) taxi-in paths to enable larger aircraft to park at gates designed for smaller aircraft, with the same level of wingtip-to-nearest-fixed-or-moving-object separations, While this approach is judged to be a viable for increasing the maximum aircraft size accommodatable and total passenger volume accommodatable at space constrained airport gates, the amount of increased airplane wingspan is limited to about 5 to 10%. Another possible disadvantage is that, for significant parking angles, modifications may need to be made to certain boarding bridges (e.g., fixed pedestal bridges) to increase the yaw swivel capability of the boarding bridgehead to assure proper sealed mating of the bridge head with the aircraft door. Or, alternatively replace the fixed pedestal bridge with an apron-drive-bridge that can swing laterally and has telescoping capability.
Yet another approach to increasing aircraft size accommodatable between adjacent parallel airport terminal piers is to replace dual, bidirectional wide-body aircraft taxilanes with unequal width dual taxilanes that re bidirectional for narrow-body aircraft (e.g., 737's and 757's) but are only unidirectional (i.e., effectively single lane) for increased span wide-body aircraft. However, this limitation could aggravate ground traffic congestion delays at major hub airports.
Finally, a seventh prior art approach to increasing aircraft size accommodatable in constrained gates and taxilanes is to equip the aircraft with foldable wingtips. This approach provides very significant airport compatibility benefits with correspondingly significant weight, complexity, and cost penalties.
As will be apparent, variations and combinations of the above-mentioned approaches are also possible.
All of the approaches cited above, except for approaches second and seventh, have the disadvantage of not allowing for increased airplane wingspan for dual bidirectional taxilanes between parallel terminal piers.